Prior to the description of the present invention, the constructions of bearings supporting a common rotating shaft of a prior art turbocharger will be described.
Referring to FIG. 1, a turbocharger 1 comprises in general a turbine casing 3 disposed on one (left) side of a bearing casing 2 and a blower casing 4 disposed on the other (right) side of the bearing casing 2. A turbine wheel 5 in the turbine casing 3 and a blower impeller 6 in the blower casing 4 are interconnected by a common rotating shaft 7 which in turn is rotatably supported by bearings 8 in the bearing casing 2. The bearing casing 2 has a lubricating oil chamber 9 through which flows a lubricating oil which lubricates the rotating shaft 7 and the bearings 8.
An oil seal 12 as shown in FIG. 2 is disposed in each of clearances 10 and 11 between the bearing casing 2 and the rotating shaft 7, thereby preventing the leakage of the lubricating oil to the exterior of the lubricating oil chamber 9.
The oil seal 12 comprises seal plates 13 and 13a, an oil thrower or slinger 14 and seal rings 15 and 15a. The seal plates 13 and 13a are securely joined to the end face 16 of the bearing casing 2 so as to surround the common rotating shaft 7 and the oil thrower or slinger 14 is disposed in the clearance between the rotating shaft 7 and the seal plates 13 and 13a. The seal rings 15 and 15a are disposed in the clearance between the sealing plates 13 and 13a and the oil thrower or slinger 14.
The oil thrower or slinger 14 is snugly fitted over the rotating shaft 7 for rotation in unison therewith. As it rotates, it attains the "slinger" effect; that is, its flange portion 14' slings the surrounding lubricating oil in the radially outward direction; so that the lubricating oil is prevented from flowing toward the seal rings 15 and 15a.
The seal rings 15 and 15a serve to prevent the lubricating oil from flowing through the clearances between the seal plates 13 and 13a on the one hand and the oil thrower or slinger 14. The rotation at high speeds of the blower impeller 6 results in the generation of a highly negative pressure in the blower casing 4 so that the lubricating oil in the chamber 9 is forcibly drawn into the blower chamber 4 through the clearances between the seal plates 13 and 13a and the oil thrower or slinger 14. Thus, the prior art oil seal has the problem that the leakage of the lubricating oil into the blower casing 4 cannot be satisfactorily prevented with the oil thrower or slinger 14 and the seal rings 15 and 15a. Leakage of lubricating oil is pronounced especially when the rotational speed of the common shaft 7 is so slow that the "slinger" effect is less.
In view of the above, the present invention has for its object to provide an oil seal for bearings of a turbocharger which can effectively prevent the leakage of a lubricating oil from a lubricating oil chamber into a blower casing and a turbine casing, especially to the former, regardless of the rotational speed of a common rotating shaft of the turbocharger.
The present invention will become more apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings.